Magnetic resonance tomography method for determining the nuclear magnetization in a number of parallel slices

Abstract

The invention relates to a fast method for the formation of a set of survey images of the nuclear magnetization in adjoining slices. First the nuclear magnetization in orthogonal slices which extend perpendicularly to the slices is excited during a plurality of successive cycles. Then the nuclear magnetization distribution for the individual slices is derived from the nuclear magnetization distribution of the orthogonal slices. Comparatively short measuring times can be achieved by means of such a method.

I claim: 
     
       1. A magnetic resonance tomography method, characterized in that for the determination of the nuclear magnetization distribution in a slice (S) first a plurality of mutually parallel slices (S') extending perpendicularly to the slice (S) are excited by cycles of sequences, each sequence including the formation of at least one slice-selective RF pulse and subsequently the switching on and off of a magnetic gradient field (Gx) extending perpendicularly to said slice (S) and also includes the reception of a spin resonance signal, the time integral over the magnetic gradient field (Gx) being varied from one cycle to another, the nuclear magnetization distribution in the mutually parallel slices (S') being determined from the spin resonance signals, the nuclear magnetization distribution in the slice (S) being determined from the distributions thus determined. 
     
     
       2. A magnetic resonance tomography method as claimed in claim 1, characterized in that within a cycle slices (S') which are situated at a distance from one another are excited by successive sequences. 
     
     
       3. A magnetic resonance tomography method as claimed in claim 1, characterized in that each sequence excites a slice (S') by means of a 90° RF pulse and a subsequent 180 ° RF pulse, the spin echo signals thus generated being used for reconstructing the nuclear magnetization distribution, the sequences of a cycle being interleaved in time so that the first RF pulse of a sequence is generated before the spin echo signal produced by the preceding sequence has been received. 
     
     
       4. A magnetic resonance tomography apparatus for for the determination of the nuclear magnetization distribution in a slice (S) in an examination zone, comprising a magnet (1) for generating a uniform, steady magnetic field in the examination zone, means for generating cycle of sequences for exciting a plurality of mutually parallel slices (S') in the examination zone, which are orthogonal to the slice (S) comprising: an RF coil system for generating magnetic RF excitation pulses in the examination zone, a gradient coil system for generating a slice-selection magnetic gradient field during said excitation pulses and for switching a magnetic gradient field on and off after the RF excitation pulse, means for receiving spin resonance signals from said examination zone, a reconstruction unit for reconstructing the nuclear magnetization distribution of the mutually parallel slices (S') from the received spin resonance signals, a storage device for storing the nuclear magnetization distributions of the plurality of mutually parallel slices (S'), and a control unit for controlling the cycles generating means in a manner that from the nuclear magnetization distributions of the plurality of mutually parallel slices the nuclear magnetization distribution of the slice (S) can be determined.